Lice are common ectoparasites of mammalian and avian species. The most important lice in domesticated animals are sucking lice (Insecta: Phthiraptera: Trichodectidae: Anoplura), which have mouthparts able to penetrate the skin of the host and enable the ingestion of tissue fluids and blood, and the chewing lice, (Insecta: Phthiraptera: Trichodectidae: Mallophaga), which predominantly ingest nutrients from the skin surface, hair, fur, wool or feathers. Chewing lice are common and economically important particularly on cattle, sheep, goats and equines and are also found on dogs, cats and birds including domesticated chickens.
Bovicola ovis, an example of a chewing louse, is a common external parasite of sheep world-wide. Infestation of sheep with this parasite has long been recognised as causing irritation of the skin with consequent rubbing and damage to the fleece (Johnson, Boray, Plant and Blunt, 1993; Lipson and Bacon-Hall, 1976). Discolouration, reduced yield and other undesirable qualities may occur in the fleeces of infested sheep (Kettle and Lukies, 1982; Kettle and Lukies, 1984; Cleland, Dobson and Meade, 1989). Additionally, recent work by the present inventors has shown that cockle, a serious defect of lambs' pelts recognised for more than 100 years (Seymour-Jones, 1913), is also associated with infestation of sheep with B. ovis (Heath, Cooper, Cole and Bishop, 1995; Heath, Cole, Bishop, Pfeffer, Cooper, and Risdon P, 1995). The inventors have further shown that cockle is characterized by a superficial perivascular dermatitis with features of an allergic response (Heath, Cole, Bishop, Pfeffer, Cooper, and Risdon P, 1995). Recent studies have supported the role of allergic immune responses to products of the louse in the development of cockle in sheep (Bany, Pfeffer, Phegan and Heath, 1995; Bany, Pfeffer and Phegan, 1995; Pfeffer, Phegan and Bany, 1997; Pfeffer, Bany, Phegan and Osborn, 1993). It can be expected that the allergic response to the louse contributes to the skin irritation that leads infested sheep to rub and damage their wool and to the skin lesions that severely devalue the pelts from affected lambs.
The economic consequences of B. ovis infestation of sheep is considerable when damage to wool and the costs of prevention of infestation are fully accounted (McLeod, 1995). To this can also be added the substantial cost of reduced quality of lambs pelts due to cockle. Apart from the direct economic costs, the continued use of conventional treatments to control louse infestation (synthetic insecticides and insect growth regulators) have detrimental effects through residues entering the environment and food chain as well as on farmer safety.
The consumer pressures to reduce the use of such harmful conventional treatments in the control of louse infestations and the development of resistance to some synthetic insecticides by lice necessitates refinement of current control strategies and a desire for new control methodologies and agents.
It is an object of the present invention to go some way towards achieving this desideratum or at least provide the public with a useful choice.
The present applicants have identified a louse antigen (allergen) that elicits an allergic response in affected sheep. The identified allergen, a protein designated Bo1, has been purified, amino acid sequenced, and the coding cDNA obtained and expressed in the bacterium, Escherichia coli. It is broadly to these allergens and their use in diagnosing, preventing and treating lice infestation and associated allergic diseases that the present invention is directed.